The invention is directed to improvements in pressure sensors having Bourdon tubes adapted to serve as an indicator means.
From U.S. Pat. No. 2,810,800, a pressure sensor is known that has a Bourdon tube curved into a helix with one fastened end and one freely movable end, which acts upon an indicator. The indicator comprises electrical contracts that are movable relative to on another. Wearing of the contacts is a disadvantage. Pressure shocks that reach the Bourdon tube and jarring affecting the pressure sensor cause vibration of the Bourdon tube and result in increased wear and incorrect indications.
In a pressure sensor known from German Auslegeschrift No. 19 55 496, a free end of a Bourdon tube acts via a wire on a free end of an elastically flexible arm the other end of which is fixed. Two strain gauges act as a contactless indicator and are part of a bridge circuit. When the arm bends elastically, this stretches one of the strain gauges elastically while compressing the other. This indicator operates in a wear-free manner. However, it is technologically difficult and expensive to fasten the wire to the Bourdon tube and th arm and there is also the danger that the wire will break during operation especially at times when the Bourdon tube begins to vibrate. The Bourdon tube itself can also be damaged or even rendered useless by vibration. No mechanical adjusting means are available, for example for performing a null drift adjustment of the indicator. As a result, a null drift adjustment can be attained only by mean of wiper contact of adjustable resistors built into the bridge circuit. Disposing transition resistors, which are vulnerable to aging, at the wiper contacts can lead to errors in measurement.